Systems and methods for alkaline earth production

ABSTRACT

Hydrometallurgical systems, methods, and compositions are described in which amine-based lixiviants are utilized in substoichiometric amounts to recover alkaline earths from raw or waste materials. The lixiviant can be regenerated and recycled for use in subsequent iterations of the process or returned to a reactor in a continuous process. Extraction of the alkaline earth from the raw material and precipitation of the extracted alkaline earth is performed in the same reactor and essentially simultaneously.

This application is a continuation-in-part of U.S. patent applicationSer. No. 14/553,640, filed Nov. 25, 2014, which is acontinuation-in-part of U.S. patent application Ser. No. 14/073,503,filed Nov. 6, 2013, and claims the benefit of priority of U.S.Provisional Application No. 61/985,036, filed Apr. 28, 2014, and U.S.Provisional Application No. 61/908,590, filed Nov. 25, 2013. These andall other referenced extrinsic materials are incorporated herein byreference in their entirety.

FIELD OF THE INVENTION

The field of the invention is hydrometallurgy, particularly as it isrelated to the extraction or recovery of alkaline earth elements.

BACKGROUND

The following description includes information that may be useful inunderstanding the present invention. It is not an admission that any ofthe information provided herein is prior art or relevant to thepresently claimed invention, or that any publication specifically orimplicitly referenced is prior art.

All publications identified herein are incorporated by reference to thesame extent as if each individual publication or patent application werespecifically and individually indicated to be incorporated by reference.Where a definition or use of a term in an incorporated reference isinconsistent or contrary to the definition of that term provided herein,the definition of that term provided herein applies and the definitionof that term in the reference does not apply.

There is a long-standing need to efficiently and cost-effectivelyrecover commercially valuable metals from low yield sources, such asmine tailings.

Historically, it has been especially desirable to recover alkaline earthelements. Alkaline earth elements, also known as beryllium groupelements, include beryllium (Be), magnesium (Mg), calcium (Ca),strontium (Sr), barium (Ba) and radium, (Ra), which range widely inabundance. Applications of these commercially important metals also varywidely, and include uses as dopants in electronic components, structuralmaterials, and in the production foods and pharmaceuticals.

Methods of isolating of one member of the alkaline earth family,calcium, from minerals such as limestone, have been known since ancienttimes. In a typical process limestone is calcined or otherwise roastedto produce calcium oxide (CaO), or quicklime. This material can bereacted with water to produce calcium hydroxide (Ca(OH)₂), or slakedlime. Calcium hydroxide, in turn, can be suspended in water and reactedwith dissolved carbon dioxide (CO₂) to form calcium carbonate (CaCO₃),which has a variety of uses. Approaches that have been used to isolateother members of this family of elements often involve the production ofinsoluble hydroxides and oxides using elevated temperatures or strongacids. Such approaches, however, are not suitable for many sources ofalkaline earth elements (such as steel slag), and are not sufficientlyselective to be readily applied to mixtures of alkaline earth elements.

Hydrometallurgy can also been used to isolate metals from a variety ofminerals, ores, and other sources. Typically, ore is crushed andpulverized to increase the surface area prior to exposure to thesolution (also known as a lixiviant). Suitable lixiviants solubilize thedesired metal, and leave behind undesirable contaminants. Followingcollection of the lixiviant, the metal can be recovered from thesolution by various means, such as by electrodeposition or byprecipitation from the solution.

Previously known methods of hydrometallurgy have several problems.Identification of lixiviants that provide efficient and selectiveextraction of the desired metal or metals has been a significanttechnical barrier to their adoption in the isolation of some metals.Similarly, the expense of lixiviant components, and difficulties inadapting such techniques to current production plants, has limited theiruse.

Approaches have been devised to address these issues. United StatesPatent Application No. 2004/0228783 (to Harris, Lakshmanan, and Sridhar)describes the use of magnesium salts (in addition to hydrochloric acid)as a component of a highly acidic lixiviant used for recovery of othermetals from their oxides, with recovery of magnesium oxide from thespent lixiviant by treatment with peroxide. Such highly acidic andoxidative conditions, however, present numerous production and potentialenvironmental hazards that limit their utility. In an approach disclosedin U.S. Pat. No. 5,939,034 (to Virnig and Michael), metals aresolubilized in an ammoniacal thiosulfate solution and extracted into animmiscible organic phase containing guanidyl or quaternary aminecompounds. Metals are then recovered from the organic phase byelectroplating.

A similar approach is disclosed in U.S. Pat. No. 6,951,960 (to Perraud)in which metals are extracted from an aqueous phase into an organicphase that contains an amine chloride. The organic phase is thencontacted with a chloride-free aqueous phase that extracts metalchlorides from the organic phase. Amines are then regenerated in theorganic phase by exposure to aqueous hydrochloric acid. Application toalkaline earth elements (for example, calcium) is not clear, however,and the disclosed methods necessarily involve the use of expensive andpotentially toxic organic solvents.

In a related approach, European Patent Application No. EP1309392 (toKocherginsky and Grischenko) discloses a membrane-based method in whichcopper is initially complexed with ammonia or organic amines. Thecopper:ammonia complexes are captured in an organic phase containedwithin the pores of a porous membrane, and the copper is transferred toan extracting agent held on the opposing side of the membrane. Such anapproach, however, requires the use of complex equipment, and processingcapacity is necessarily limited by the available surface area of themembrane.

Methods for capturing CO₂ could be used to recover alkaline earthmetals, but to date no one has appreciated that such could be done.Kodama et al. (Energy 33 (2008), 776-784) discloses a method for CO₂capture using a calcium silicate (2CaO.SiO₂) in association withammonium chloride (NH₄Cl). This reaction forms soluble calcium chloride(CaCl₂), which is reacted with carbon dioxide (CO₂) under alkalineconditions to form insoluble calcium carbonate (CaCO₃) and releasechloride ions (Cl−).

Kodama et al. uses clean forms of calcium to capture CO₂, but is silentin regard to the use of other alkaline earth elements in this chemistry.That makes sense from Kodoma et al.'s disclosure, which notes that ahigh percentage (approximately 20%) of the NH₄Cl used is lost in thedisclosed process, requiring the use of additional equipment to captureammonia vapor. This loss results in significant process inefficiencies,and raises environmental concerns. Japanese Patent Application No.2005097072 (to Katsunori and Tateaki) discloses a similar method for CO₂capture, in which ammonium chloride (NH₄Cl) is dissociated into ammoniagas (NH₃) and hydrochloric acid (HCl), the HCl being utilized togenerate calcium chloride (CaCl₂) that is mixed with ammonium hydroxide(NH₄OH) for CO₂ capture.

International Application WO 2012/055750 (to Tavakkoli et al) disclosesa method for purifying calcium carbonate (CaCO₃), in which impure CaCO₃is converted to impure calcium oxide (CaO) by calcination. The resultingCaO is treated with ammonium chloride (NH₄Cl) to produce calciumchloride (CaCl₂), which is subsequently reacted with high purity carbondioxide (CO₂) to produce CaCO₃ and NH₄Cl, with CaCO₃ being removed fromthe solution by crystallization with the aid of seed crystals. Withoutmeans for capturing or containing the ammonia gas that would result fromsuch a process, however, it is not clear if the disclosed method can beadapted to an industrial scale.

Thus, there is still a need for a hydrometallurgical method thatprovides simple and economical isolation of metal hydroxide formingspecies.

SUMMARY OF THE INVENTION

The inventive subject matter provides hydrometallurgical systems,methods, and compositions in which amine-based lixiviants are utilizedin substoichiometric amounts to recover alkaline earths from raw orwaste materials. The lixiviant can be regenerated and recycled for usein subsequent iterations of the process or returned to a reactor in acontinuous process. Extraction of the alkaline earth from the rawmaterial and precipitation of the extracted alkaline earth is performedin the same reactor and essentially simultaneously.

One embodiment of the inventive concept is a method for recovering analkaline earth (for example, calcium) from an alkaline earth-bearing rawmaterial or waste product. In such a method the raw material (forexample, a steel slag), an amine containing lixiviant, and a precipitant(i.e. a compound that reacts with an alkaline earth released from theraw material to form a precipitate, for example a gas that contains CO₂)are brought into contact in reactor. The lixiviant is provided insubstoichiometric amounts relative to the amount of alkaline earthavailable in the raw material. The subsequent series of reactionsproduces an alkaline earth precipitate and an extracted raw material,and in the process regenerates the lixiviant species. The alkaline earthprecipitate and the extracted raw material are separated, and some orall of the regenerated lixiviant is returned to the reactor.

The alkaline earth precipitant and the extracted raw material can beseparated on the basis of particle size/diameter, particle density,and/or differential magnetic properties. Suitable separators includesettling tanks filters, centrifugal separators, and magnetic separators.For example the reactor, or a portion thereof, can be configured as asettling tank. In some embodiments the separation is performed on abatch basis. In other embodiments the separation is performed on acontinuous basis.

In some embodiments of the inventive concept, the raw material, thelixiviant, and/or the precipitant are added to the reactor in anessentially continuous manner. Similarly, in other embodiments of theinventive concept the separation process is performed in an essentiallycontinuous manner.

In still other embodiments of the inventive concept the extracted rawmaterial, which is relatively enriched in non-extracted elementsfollowing extraction of the alkaline earth component, is not discarded,but rather is retained and subjected to further processing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an example of a method of the inventive concept in whichcalcium is recovered from a sample, using an organic amine chloridelixiviant that is regenerated.

FIG. 2 schematically depicts a method of the inventive concept, in whicha alkaline earth elements is recovered from a sample using a lixiviant,which is regenerated.

FIG. 3 schematically depicts another method of the inventive concept, inwhich different alkaline earth elements are recovered in a stepwisefashion.

FIG. 4 schematically depicts an alternative embodiment of the inventiveconcept, in which different alkaline earth elements are recovered in astepwise manner.

FIG. 5 illustrates the composition of a steel slag.

FIG. 6 schematically depicts processing of a steel slag by a method ofthe inventive concept.

FIG. 7A-D show the results of systems, methods, and compositions of theinventive concept. FIG. 7A shows pH changes over time as an alkalineearth element is extracted from a low grade source using an organicamine lixiviant. FIG. 7B shows pH changes over time as an alkaline earthelement is extracted from a low grade source using a different organicamine lixiviant. FIG. 7C shows pH changes over time as an extractedalkaline earth element is recovered through the use of a precipitant.FIG. 7D is a photomicrograph of a precipitated calcium carbonate productof systems, methods, and compositions of the inventive concept.

FIG. 8A-E show a prior art commercial plant and a commercial plantadapted to utilize a process of the inventive concept. FIG. 8A depictscomponents and material flow in a prior art processing plant. FIG. 8Bdepicts components and material flow in a processing plant that has beenmodified to perform a process of the inventive concept. FIG. 8C depictsthe use of multi-effect evaporators in a modified plant such as thatshown in FIG. 8B. FIG. 8D and FIG. 8E schematically depict exemplarymass balances and reaction conditions for processes of the inventiveconcept applied to steel slag and to lime, respectively.

FIGS. 9A and 9B schematically depict a single-step method of theinventive concept, wherein extraction of the alkaline earth andprecipitation are not segregated. FIG. 9A depicts a method that utilizesa lixiviant. FIG. 9B depicts a method in that does not include an addedlixiviant.

FIGS. 10A and 10B schematically depict an alternative single-step methodof the inventive concept, wherein extraction of the alkaline earth andprecipitation are not segregated. FIG. 10A depicts a method thatutilizes a lixiviant. FIG. 10B depicts a method in that does not includean added lixiviant.

FIG. 11 schematically depicts an alternative embodiment of a method ofthe inventive process, wherein extraction of the alkaline earth andprecipitation are partially segregated.

FIG. 12A and FIG. 12B show exemplary results from one-step and two-stepmethods of alkaline earth recovery. FIG. 12A shows recovery of calciumin the form of calcium carbonate from two different steel slags. FIG.12B shows the increase in yield of calcium carbonate from a one-stepprocess compared to a prior art two-step process from two differentsteel slags as a function of the particle size of the respective steelslags.

FIG. 13 shows the distribution of different products from a single-stepmethod of the inventive concept as a function of the particle size ofthe raw material.

FIG. 14 shows the yield of calcium in the form of calcium carbonate atdifferent ratios of amine lixiviant to calcium available in the rawmaterial.

FIG. 15 shows the distribution of different products from a single-stepmethod of the inventive concept at different ratios of amine lixiviantto calcium available in the raw material.

FIG. 16 shows exemplary results from pH monitoring during a prior arttwo-step method.

FIG. 17A and FIG. 17B show exemplary results from pH monitoring during asingle-step method of the inventive concept. FIG. 17A shows the changein pH on suspension of raw material (1), addition of lixiviant (2),first addition of CO₂ (3), cessation of CO₂ (4), second addition of CO₂(5), and termination (6). FIG. 17B shows a detail of pH changes during aCO₂ addition at different lixiviant:alkaline earth ratios and withdifferent sources of raw material.

FIG. 18 depicts the increase in the amount of steel slag raw materialrequired to produce one ton of calcium carbonate by the traditionaltwo-step method over the amount required by a one-step method of theinventive concept.

FIG. 19 depicts a table showing the composition of different steelslags.

FIG. 20 depicts a table showing experimental conditions used in two-stepand one-step processes.

DETAILED DESCRIPTION

The inventors have discovered a hydrometallurgical method for therecovery of alkaline earth elements (i.e., alkaline earth metals), suchas members of the alkaline earth family, through the use of lixiviantsthat include organic amines. The inventors have determined that suchamine-based lixiviants can be regenerated using carbon dioxide.Surprisingly, this regeneration permits extraction of an alkaline earthfrom a raw material and precipitation of the extracted alkaline earth,for example in the form of a carbonate, in the same reactor andessentially simultaneously, with differences between the physicalproperties of the carbonate salt produced and the extracted raw materialpermitting separation by simple physical means.

Throughout the following discussion, numerous references will be maderegarding lixiviants. A lixiviant should be understood to be a chemicalentity that has the ability to selectively extract metals or metal ionsfrom inorganic or organic solids in an aqueous or other solvent mixture.Similarly, a precipitant should be understood to be a chemical entitythat has the ability to form a precipitate that includes such extractedmetals or metal ions.

The following discussion provides many exemplary embodiments of theinventive subject matter. Although each embodiment represents a singlecombination of inventive elements, the inventive subject matter isconsidered to include all possible combinations of the disclosedelements. Thus if one embodiment comprises elements A, B, and C, and asecond embodiment comprises elements B and D, then the inventive subjectmatter is also considered to include other remaining combinations of A,B, C, or D, even if not explicitly disclosed.

In some embodiments, the numbers expressing quantities of ingredients,properties such as concentration, reaction conditions, and so forth,used to describe and claim certain embodiments of the invention are tobe understood as being modified in some instances by the term “about.”Accordingly, in some embodiments, the numerical parameters set forth inthe written description and attached claims are approximations that canvary depending upon the desired properties sought to be obtained by aparticular embodiment. In some embodiments, the numerical parametersshould be construed in light of the number of reported significantdigits and by applying ordinary rounding techniques. Notwithstandingthat the numerical ranges and parameters setting forth the broad scopeof some embodiments of the invention are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspracticable. The numerical values presented in some embodiments of theinvention may contain certain errors necessarily resulting from thestandard deviation found in their respective testing measurements.Similarly, unless the context dictates the contrary all ranges set forthherein should be interpreted as being inclusive of their endpoints andopen-ended ranges should be interpreted to include only commerciallypractical values. Similarly, all lists of values should be considered asinclusive of intermediate values unless the context indicates thecontrary.

As used in the description herein and throughout the claims that follow,the meaning of “a,” “an,” and “the” includes plural reference unless thecontext clearly dictates otherwise. Also, as used in the descriptionherein, the meaning of “in” includes “in” and “on” unless the contextclearly dictates otherwise.

The recitation of ranges of values herein is merely intended to serve asa shorthand method of referring individually to each separate valuefalling within the range. Unless otherwise indicated herein, eachindividual value with a range is incorporated into the specification asif it were individually recited herein. All methods described herein canbe performed in any suitable order unless otherwise indicated herein orotherwise clearly contradicted by context. The use of any and allexamples, or exemplary language (e.g. “such as”) provided with respectto certain embodiments herein is intended merely to better illuminatethe invention and does not pose a limitation on the scope of theinvention otherwise claimed. No language in the specification should beconstrued as indicating any non-claimed element essential to thepractice of the invention.

Embodiments of the inventive process can include at least one compoundof the general composition depicted as in Compound 1 for use with anysource of material that contains one or more a form(s) of a alkalineearth (AE) hydroxide forming species, that can be hydrated to formAE(OH)x or other hydrated species that would react with lixiviants ofthe form found in Equation 1. Alternatively, alkaline earth elements canbe presented as oxides, for example calcium oxide (CaO), that can formhydroxides on reaction with water. Such hydrated forms may be present inthe material as it is obtained from nature or can be introduced byprocessing (for example through treatment with a base, hydration, or byoxidation), and can be stable or transient. Selective extraction of adesired alkaline earth can be based on the presence of a metal hydroxidethat has a stronger basicity than the organic amine-based lixiviantsused in the extraction process.

Organic amines of the inventive concept have the general formula shownin Compound 1, where N is nitrogen, H is hydrogen, R₁ to R₃ can be anorganic (i.e. carbon-containing) group or H, and X is a counterion(i.e., a counter anion).

Ny,R₁,R₂,R₃,H—Xz  Compound 1

Suitable counterions can be any form or combination of atoms ormolecules that produce the effect of a negative charge. Counterions canbe halides (for example fluoride, chloride, bromide, and iodide), anionsderived from mineral acids (for example nitrate, phosphate, bisulfate,sulfate, silicates), anions derived from organic acids (for examplecarboxylate, citrate, malate, acetate, thioacetate, propionate and,lactate), organic molecules or biomolecules (for example acidic proteinsor peptides, amino acids, nucleic acids, and fatty acids), and others(for example zwitterions and basic synthetic polymers). For example,monoethanolamine hydrochloride (MEA.HCl, HOC₂H₄NH₃Cl) conforms toCompound 1 as follows: one nitrogen atom (N₁) is bound to one carbonatom (R₁=C₂H₅O) and 3 hydrogen atoms (R₂, R₃ and H), and there is onechloride counteranion (X₁=Cl−). Compounds having the general formulashown in Compound 1 can have a wide range of acidities, and an organicamine of the inventive concept can be selected on the basis of itsacidity so that it can selectively react with one or more alkaline earthmetal salts or oxides from a sample containing a mixture of alkalineearth metal salts or oxides. Such a compound, when dissolved in water oranother suitable solvent, can (for example) effectively extract thealkaline earth element calcium presented in the form calcium hydroxidein a suitable sample (e.g. steel slag). Equation 1 depicts a primarychemical reaction in extracting an insoluble alkaline earth (AE) salt(in this instance a hydroxide salt) from a matrix using an organic aminecation (OA-H+)/counterion (Cl−) complex (OA-H+/Cl−) as a lixiviant. Notethat the OA-H+/Cl− complex dissociates in water into OA-H+ and Cl−.

AE(OH)₂(solid)+2OA-H+(aq)+2Cl−(aq)→AECl₂(aq)+2OA(aq)+2H₂O  Equation 1

The counterion (Cl−) is transferred from the organic amine cation(OA-H+) to the alkaline earth salt to form a soluble alkalineearth/counterion complex (AECl₂), uncharged organic amine (OA), andwater. Once solubilized the alkaline earth/counterion complex can berecovered from solution by any suitable means. For example, addition ofa second counterion (SC) in an acid form (for example. H₂SC), whichreacts with the alkaline earth cation/counterion complex to form aninsoluble alkaline earth salt (AESC), can be used to precipitate theextracted alkaline earth from supernatant and release the counterion toregenerate the organic amine cation/counterion pair, as shown inEquation 2.

AECl₂(aq)+2OA(aq)+H₂SC→AESC salt(solid)+2OA+(aq)+2Cl−  Equation 2

Examples of suitable second counterions include polyvalent cations, forexample carbonate (which can be supplied as CO₂), sulfate, sulfite,chromate, chlorite, and hydrogen phosphate.

Alternatively, pH changes, temperature changes, or evaporation can beused to precipitate the solubilized alkaline earth. In some embodiments,the alkaline earth element can be recovered by electrodepositionprocesses, such as electrowinning or electrorefining. In otherembodiments of the inventive concept the solubilized alkaline earthelement can be recovered by ion exchange, for example using a fixed bedreactor or a fluidized bed reactor with appropriate media.

In preferred embodiments of the inventive concept, an alkaline earthelement is recovered by precipitation through reaction of the alkalineearth/lixiviant mixture with carbon dioxide (CO₂), which advantageouslyregenerates the lixiviant as shown below. It should be appreciated thatthe process of recovering the alkaline earth element can be selective,and that such selectivity can be utilized in the recovery of multiplealkaline earth elements from a single source as described below.

The organic amine cation/counterion complex can be produced from theuncharged organic amine to regenerate the OA-H+/Cl− lixiviant, forexample using an acid form of the counterion (H—Cl), as shown inEquation 3.

OA(aq)+H−Cl(aq)→OA-H+(aq)+Cl−  Equation 3

In some embodiments of the inventive concept the reaction described inEquation 3 can be performed after the introduction of an unchargedorganic amine to a source of an alkaline earth element, with thelixiviant being generated afterwards by the addition of an acid form ofthe counterion. This advantageously permits thorough mixing of thealkaline earth source with a lixiviant precursor prior to initiating thereaction.

Organic amines suitable for the extraction of alkaline earth elements(for example from calcium containing or, steel slag, and othermaterials) can have a pKa of about 7 or about 8 to about 14, and caninclude protonated ammonium salts (i.e., not quaternary). Examples ofsuitable organic amines for use in lixiviants include weak bases such asammonia, nitrogen containing organic compounds (for examplemonoethanolamine, diethanolamine, triethanolamine, morpholine, ethylenediamine, diethylenetriamine, triethylenetetramine, methylamine,ethylamine, propylamine, dipropylamines, butylamines, diaminopropane,triethylamine, dimethylamine, and trimethylamine), low molecular weightbiological molecules (for example glucosamine, amino sugars,tetraethylenepentamine, amino acids, polyethyleneimine, spermidine,spermine, putrecine, cadaverine, hexamethylenediamine,tetraethylmethylenediamine, polyethyleneamine, cathine, isopropylamine,and a cationic lipid), biomolecule polymers (for example chitosan,polylysine, polyornithine, polyarginine, a cationic protein or peptide),and others (for example a dendritic polyamine, a polycationic polymericor oligomeric material, and a cationic lipid-like material), orcombinations of these. In some embodiments of the inventive concept theorganic amine can be monoethanolamine, diethanolamine, ortriethanolamine, which in cationic form can be paired with nitrate,bromide, chloride or acetate anions. In other embodiments of theinventive concept the organic amine can be lysine or glycine, which incationic form can be paired with chloride or acetate anions. In apreferred embodiment of the inventive concept the organic amine ismonoethanolamine, which in cationic form can be paired with a chlorineanion.

Such organic amines can range in purity from about 50% to about 100%.For example, an organic amine of the inventive concept can have a purityof about 50%, about 55%, about 60%, about 65%, about 70%, about 75%,about 80%, about 85%, about 90%, about 95%, about 97%, about 99%, orabout 100%. In a preferred embodiment of the inventive concept theorganic amine is supplied at a purity of about 90% to about 100%. Itshould be appreciated that organic amines can differ in their ability tointeract with different members of the alkaline earth family and withcontaminating species, and that such selectivity can be utilized in therecovery of multiple alkaline earths as described below.

Inventors further contemplate that zwitterionic species can be used insuitable lixiviants, and that such zwitterionic species can formcation/counterion pairs with two members of the same or of differentmolecular species. Examples include amine containing acids (for exampleamino acids and 3-aminopropanoic acid), chelating agents (for exampleethylenediamine-tatraacetic acid and salts thereof, ethylene glycoltetraacetic acid and salts thereof, diethylene triamine pentaacetic acidand salts thereof, and1,2-bis(o-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid and saltsthereof), and others (for example betaines, ylides, andpolyaminocarboxylic acids).

Organic amines for use in lixiviants can be selected to have minimalenvironmental impact. The use of biologically derived organic amines,such as glycine, is a sustainable practice and has the beneficial effectof making processes of the inventive concept more environmentally sound.In addition, it should be appreciated that some organic amines, such asmonoethanolamine, have a very low tendency to volatilize duringprocessing. In some embodiments of the inventive concept an organicamine can be a low volatility organic amine (i.e., having a vaporpressure less than or equal to about 1% that of ammonia under processconditions). In preferred embodiments of the inventive concept theorganic amine is a non-volatile organic amine (i.e., having a vaporpressure less than or equal to about 0.1% that of ammonia under processconditions). Capture and control of such low volatility and non-volatileorganic amines requires relatively little energy and can utilize simpleequipment. This reduces the likelihood of such low volatility andnon-volatile organic amines escaping into the atmosphere andadvantageously reduces the environmental impact of their use.

An example of an application of the inventive concept is in theisolation of insoluble calcium hydroxide, using an ammonium chloridecontaining lixiviant or, alternatively, in the absence of an addedlixiviant. Any source that contains a basic form of calcium can besuitable for use in a process of the inventive concept, for example orescontaining alkaline earth oxides and/or hydroxide calcined orescontaining alkaline earth oxides and/or hydroxides, partially calcinedores containing alkaline earth oxides and/or hydroxides, steel slag, flyash, cement kiln dust, ash, shale ash, acetylene catalyst waste, dolime,lime, low-grade lime, ash from municipal waste, and calcium hydroxide.In some embodiments of the inventive concept a calcium source can beselected on the basis of high calcium content per unit mass with highlevels of contamination, for example low grade lime or dolomitic lime.In other embodiments of the inventive concept, calcium can be recoveredfrom lime, for example low grade lime. Equation 4 represents a reactionthat takes place on contacting calcium hydroxide (Ca(OH)₂))-containingsteel slag with an ammonium chloride lixiviant.

Ca(OH)₂(solid)+2NH₄+(aq)+2Cl−(aq)→CaCl₂(aq)+2NH₃(aq)+2H₂O  Equation 4

Calcium is extracted from the slag as soluble calcium chloride (CaCl₂),with the generation of uncharged ammonia (NH₃) and water.

A soluble alkaline earth salt, for example calcium chloride and thesoluble ammonia from Equation 4 (or soluble ammonium ion if the reactionis metal oxide/hydroxide limited) can easily be separated from theinsoluble solid residue, for example by filtration. Once separated, thesoluble aqueous fraction can be used as-is if the target process cantolerate the small quantity of ammonia or ammonium chloride.Alternatively, the solution can be further processed as needed. In apreferred embodiment of the inventive concept the lixiviant isregenerated and the alkaline earth calcium is recovered as an insolublesalt through the addition of carbon dioxide (CO₂), as shown in Equation5. It should be appreciated that aqueous CO₂ can be in the form ofionized carbonic acid (i.e., 2H+ plus CO₃2−).

CaCl₂(aq)+2NH₃(aq)+CO₂(aq)+H₂O→CaCO₃(solid)+2NH₃(aq)++2Cl−(aq)  Equation5

It should be appreciated that systems, methods, and compositions of theinventive concept can also be used to selectively extract and/or refinea desired alkaline earth element (such as calcium) from an orecontaining other contaminants, for example other alkaline earthelements. By using the lixiviants described herein, one skilled in theart can exploit the varying degrees of basicity associated with eachalkaline earth element, and choose a lixiviant of corresponding acidityto achieve selective extraction.

As noted above, in many instances the use of a low volatility and/ornon-volatile lixiviant is desirable. An example of such a process of theinventive concept is the extraction of calcium (Ca) from an ore using anon-volatile organic amine, such as monoethanolamine hydrochloride, asshown in FIG. 1. FIG. 1 depicts a process 100 in which, in an initialstep 105, a tank or other suitable arrangement includes an aqueoussolution of an organic amine 110 (in this instance monoethanolamine) anda mud or slurry 120 containing calcium hydroxide (Ca(OH)₂ and unwantedcontaminants (CONT). The solvent used can be any protic or highly polarsolvent that can support the solvation of calcium salts in largeamounts. Examples of suitable solvents include water, glycerol, andwater glycerol mixtures. The amount of organic amine can be optimizedfor efficient alkaline earth extraction and minimal use of organicamine. For example, in some embodiments the amount of a monovalentorganic amine can be selected to be at least about twice that of theavailable alkaline earth element on a molar basis. In some embodimentsof the inventive concept the amount of a monovalent organic amine can beselected to be at least about 2.1 times to about 2.05 times that of theavailable alkaline earth element. Amounts of organic amines with greatercharges can be adjusted accordingly (for example, an organic amine thatforms a divalent cation can be used in at least a 1:1 ratio with theavailable alkaline earth element). Alternatively, and as described infurther detail below, regeneration of the lixiviant species can permitthe lixiviant species to be utilized in sub-stoichiometric amounts.

Reaction conditions can also be optimized by adjusting the surface areaavailable for the reaction. Particle size of the calcium containing rawmaterial can be reduced prior to exposure to lixiviant, for example bygrinding, milling, or sifting. In some embodiments of the inventiveconcept the particle size can range from about 0.05 mm to about 1 mm. Inother embodiments of the inventive concept the particle size can rangefrom about 0.05 to about 0.25 mm. In a preferred embodiment the particlesize can range from about 0.05 mm to about 0.125 mm.

The calcium content of the solution can also be adjusted to provideefficient extraction. In some embodiments of the inventive concept theCa content is controlled such that the mass ratio of Ca (in terms of CaOto water) can range from about 0.02 to about 0.5. In other embodimentsthe mass ratio of Ca can range from about 0.05 to about 0.25. In apreferred embodiment of the inventive process the mass ratio of Ca canrange from about 0.1 to about 0.15.

The extraction process can be initiated as shown in 125 by the additionof an acid form of a counterion 130, in this instance hydrochloric acid(HCl), which generates an organic acid cation/counterion pair 140 (inthis instance monoethanolamine hydrochloride (MEA+/Cl−)) to form alixiviant solution. Monoethanolamine hydrochloride (MEA.HCl,HOC₂H₄NH₃Cl) conforms to Compound 1 as follows: one nitrogen atom (N₁)is bound to one carbon atom (R₁=C₂H₅O) and 3 hydrogen atoms (R₂, R₃ andH), and there is one chloride counteranion (X₁=Cl−). The extractionprocess can be performed at any temperature suitable to supportsolvation of the alkaline earth salt formed by reaction with the organicamine cation/counterion pair. In some embodiments of the inventiveconcept the extraction can be performed in a temperature range of about0° C. to about 120° C. In other embodiments of the inventive concept theextraction can be performed within a temperature range of about 20° C.to about 100° C. In a preferred embodiment of the inventive concept theextraction can be performed within a temperature range of about 20° C.and about 70° C., advantageously reducing the need for temperaturecontrol equipment.

As shown in 145 the lixiviant can enter or mix with the mud/slurry and,as shown in FIG. 1, effectively extract an alkaline earth hydroxide, forexample calcium hydroxide (Ca(OH)₂), by the formation of a solublealkaline earth cation/counterion pair 150 (in this instance, calciumchloride (Ca(Cl)₂)). The reaction can be stirred during the extractionprocess in order to improve reaction kinetics. In some embodimentsstirrer speeds can range from about 100 rpm to about 2000 rpm; in otherembodiments of the inventive concept stirrer speeds can range from about200 rpm to about 500 rpm. Equation 6 depicts a critical chemicalreaction in such an extraction (in this case calcium, from steel slagthat contains contaminants). Note that MEA.HCl dissociates in water intomonoethanolammonium cation (HOC₂H₄NH₃+ (MEAH+)) and chloride anion(Cl−). Reaction products include soluble CaCl₂ and unchargedmonoethanolamine (MEA)).

Ca(OH)₂(s)+2HOC₂H₄NH₃+(aq)+2Cl−(aq)→CaCl₂(aq)+2HOC₂H₄NH₂(aq)+2H₂O(l)  Equation6

The extraction process can be performed for any suitable length of time,as defined by the amount and quality of the material to be processed. Insome embodiments of the inventive concept the extraction can beperformed for 0.5 hours to 24 hours. In other embodiments the extractioncan be performed for about 30 minutes. In preferred embodiments of theinventive concept the extraction can be performed for about 15 minutes.Depending in part on the organic amine species used in the lixiviant,the pH of the solution can change during the extraction process, forexample increasing as the alkaline earth element is extracted from thesample. In some embodiments of the inventive concept the pH of thesolution at the beginning of the extraction can range from about 6 toabout 13. In other embodiments of the inventive concept the pH at theend of the extraction step can range from about 10 to about 12.

Extraction of a sample with a lixiviant leaves insoluble materials thatare not desirable in the final product. These can be removed by avariety of means, including settling, centrifugation, and filtration, asin 165 of step 155. In preferred embodiments of the inventive conceptinsoluble materials are removed by filtration, for example in a filterpress that produces a filter cake. In order enhance the efficiency ofthe process, a filter cake from such a filtration can be washed toremove additional extracted calcium. In some embodiments the filter cakecan be treated with a wash volume that is about 10 times that of thewetness of the filter cake. In preferred embodiments of the inventiveprocess lower volumes can be used, for example about 5 times that of thewetness of the filter cake or about 3 times that of the wetness of thefilter cake.

Following separation of the soluble fraction or supernatant from theunreacted contaminants 165, the solubilized alkaline earth element canbe recovered by the addition of a precipitant 170, for example carbondioxide (CO₂), as shown in 175. The precipitant acts to form aninsoluble salt with the alkaline earth element. Suitable precipitantsinclude, but are not limited to, carbon dioxide, carbonate, bicarbonate,sulfate, and phosphate, and can be supplied as a gas (e.g. CO₂), salt,or acid. Accordingly, it should be understood that, while carbonatesalts of alkaline earth elements are widely used as examples throughoutthis document, corresponding sulfate and/or phosphates salts areconsidered to be included in the inventive concept.

Surprisingly, inventors have found that CO₂ precipitation of alkalineearth chlorides (for example, CaCl₂) can proceed efficiently at anacidic pH (i.e., pH<7). Addition of CO₂ also generates the organic aminecation/counterion pair, as shown in 190 and in Equation 7, therebyregenerating the lixiviant.

CaCl₂(aq)+2HOC₂H₄NH₂(aq)+2H₂O(l)+CO₂→CaCO₃(solid)+HOC₂H₄NH₃+(aq)+Cl−  Equation7

In the exemplary reaction the precipitant forms calcium carbonate(CaCO₃) 180 which, being relatively insoluble, can be easily recoveredfor additional processing and, if desired, recovery of calcium. Forexample, CaCO₃ can be recovered using a filter press, as describedabove. The regenerated lixiviant can be recycled into the process 185,advantageously reducing the overall need for lixiviant and increasingprocess efficiency as more raw materials containing alkaline earths areprocessed.

The precipitation reaction can be performed at any temperature suitableto support the solubility of the precipitating agent (for example, CO₂)and maintain the insolubility of the precipitated salt. In someembodiments of the inventive concept the precipitation reaction can beperformed at about 4° C. to about 100° C. In other embodiments theprecipitation reaction can be performed at about 20° C. to about 80° C.In preferred embodiments of the inventive concept the precipitation canbe performed at about 40° C. to about 80° C. The concentration of CO₂gas supplied can range from about 0.1% to about 100%. In someembodiments of the inventive concept the concentration of CO₂ gas canrange from 10% to about 100%. This advantageously permits relatively lowquality sources of CO₂, for example flue gas or other waste gases, to beutilized. The CO₂-containing gas can be applied at any rate suitable forconversion of essentially all of the calcium present to CaCO₃ within asuitable time, for example about 3 hours to about 4 hours. Suitable flowrates can range from 1 L/hour/mol Ca to about 100 L/hr/mol Ca. Inpreferred embodiments of the inventive concept the flow rate for CO₂containing gas can be about 10 L/hour/mol Ca to about 20 L/hour/mol Ca.The pH of the solution can change during the precipitation reaction.

The pH of a working solution can change during the precipitation step.In some embodiments of the inventive concept, the starting pH of thesolution can range from about 9 to about 12, and can range from about 6to about 8 at the end of the precipitation. Advantageously, this pHshift can be monitored to provide an indication of the progress of aprecipitation reaction. Surprisingly, inventors have found that such aCO₂ precipitation of alkaline earth chlorides (for example, CaCl₂) inthis process can proceed efficiently at an acidic pH (i.e., pH<7). Theprecipitation reaction can be performed until a suitable endpoint isreached. For example, in some embodiments the precipitation can beperformed until the pH of the reaction remains below a specifiedsetpoint (for example, a pH of about 8) for at least about 15 minutes.

Separation of the precipitate can be accomplished by any suitablemethod, including removing the soluble fraction from the tank (forexample, by decanting, pumping, or siphoning), filtration,centrifugation or other application of centripetal force, or acombination of these. In some embodiments the precipitate is removedusing a filter press. The resulting filter cake can be easily recoveredfor additional processing and, if desired, recovery of calcium. Theregenerated lixiviant can be recycled into the next iteration of theprocess 185, advantageously reducing the overall need for lixiviant andincreasing process efficiency as more raw materials containing alkalineearths are processed.

It should be noted that the choice of lixiviant can allow for theselective extraction of calcium in this example because it does notreact with other metals (ME) or metal oxides/hydroxides (MEO_(x)) in thealkaline earth source material, as shown in Equation 8 and Equation 9.

ME(s)+HOC₂H₄NH₃+(aq)→NO REACTION  Equation 8

MEO_(x)(s)+HOC₂H₄NH₃+(aq)→NO REACTION  Equation 9

The soluble calcium salt and the soluble MEA from Equation 6 can easilybe separated from the insoluble solid residue. Once separated, thesoluble aqueous fraction can used as-is if the target process canwithstand the small quantity of lixiviant as a contaminant, or thesolution can be furthered processed as needed.

In an alternative embodiment of the inventive concept, a solutioncontaining an alkaline earth cation/counterion complex as shown inEquation 6 can be concentrated or diluted to a desired strength asrequired by the end user. Alternatively, such a solution can be boileddown or evaporated completely, leaving an alkaline earth elementcation/counterion salt and/or various hydrates thereof, depending on howvigorously the mixture is dried. The residual uncharged organic aminecould also be removed by this process and optionally captured for reuse.The dried alkaline earth element chlorides could be further processedinto oxides via thermal oxidation, precipitation with agents such oxalicacid, sodium hydroxide, potassium hydroxide or other precipitatingagents.

There are of course many possible lixiviants of the form of Compound 1,and there are likewise many alkaline earth element sources. While theexamples provided have described the action of two organic aminelixiviants (i.e., ammonium chloride and monoethanolamine hydrochloride(a.k.a. monoethanolammonium chloride) with one particular source (steelslag) of a particular alkaline earth element (calcium) other examples ofprocess of the inventive concept can utilize organic aminecation/counterion pairs such as ammonium acetate, monoethanolammoniumacetate, ammonium nitrate, or monoethanolammonium nitrate.Alternatively, biologically derived lixiviants such as the amino acidglycine (or a salt of itself) or the hydrobromide salt of poly-L-lysinecan be used. Similarly, while examples note the use of steel slag, othersources (such as calcite, dolomite, gypsum, plagioclases, amphiboles,pyroxenes, and garnets) are suitable. Alternatively, systems, methods,and compositions of the inventive concept can be utilized to recoveralkaline earth elements from agricultural waste, consumer waste,industrial waste, scrap or other excess materials from manufacturingprocesses, or other post-utilization sources.

Many alkaline earth elements can form hydroxides; most of these havevery limited solubility in water. These hydroxides also have varyingdegrees of basicity. While calcium hydroxide as produced from variousmineral sources has been cited as an example there are many otheralkaline earth elements that form suitable bases in water. Examples ofother elements that, in hydroxide form, are suitable for use in systemsand methods of the inventive concept include beryllium, magnesium,strontium, barium, and radium. Such salts have different basicities,which can be paired with organic amine based lixiviants of differentacidities to provide selective recovery.

It should also be noted that systems, methods, and compositions of theinventive concept are not limited to one alkaline earth species beingextracted with one particular lixiviant or set of anions. Multiplealkaline earth species with various organic amine based lixiviants andvarious anions (or acids) can be used in sequence or in parallel toextract a particular mixture of metals or to produce a particularmixture of metal salts.

As described above, lixiviants of the inventive concept can be appliedin a variety of methods. Examples of some of these methods are depictedschematically in FIG. 2, FIG. 3, and FIG. 4.

FIG. 2 depicts a method of the inventive process 200 in which a sample210, for example an ore, mineral, or other source of an alkaline earthelement, is mixed with a lixiviant 220. The lixiviant can include one ormore organic amine species as described above in the form of a cation,coupled with a suitable counterion. Suitable counterions can includehalides. In a preferred embodiment of the inventive concept thecounterion is chloride (Cl−).

A sample 210 can be a calcium-containing ore (for example dolomite orgypsum), a byproduct of a manufacturing process (for example, steelslag), or any suitable calcium source. The sample 210 can be treatedprior to mixing with the lixiviant 220. For example, the components ofthe sample 210 can be reduced in size, for example through milling,grinding, pulverizing, or sifting. Such processes improve the surfacearea to volume ratio of elements of the sample and can serve to increasereaction rates. In some embodiments a sample can be chemically treated,for example through exposure to strong bases (such as sodium hydroxide)or oxidized through exposure to air at elevated temperatures. Suchchemical treatments can serve to generate alkaline earth metal salts(for example, hydroxides or oxides) and to alter the physical structureof the sample or components of the sample.

On interacting with the lixiviant 220, alkaline earth elements in thesample interact with organic amine cations and counterions to form asoluble alkaline earth element cation/counterion complex that issolubilized in the supernatant 230, along with an uncharged organicamine. The pH of this portion of the reaction process can be alkaline,i.e., ranging from about 7.5 to about 14. In some embodiments of theinventive concept the pH can range from about 10 to about 12. Unwantedcontaminants are not solvated, and remain behind as insoluble material,for example as a treated sample 240 that can be further processed ifdesired.

The supernatant 250 can be separated from the insoluble materials of thetreated sample 240 by a variety of processes, including settling,filtration, or centrifugation, either alone or in combination. Thealkaline earth cation 260 can be recovered from the supernatant 250 byany suitable means, including electrodeposition, precipitation, and ionexchange. In a preferred embodiment of the inventive concept thealkaline earth cation is recovered by the addition of a precipitant (Pr)to produce an insoluble alkaline earth salt that is easily recovered.Such precipitants can be an H+ donating species suitable for forminginsoluble salts of alkaline earth elements while regenerating an organicamine cation, for example CO₂ or carbonic acid, chromic acid, orsulfuric acid. In a preferred embodiment of the inventive concept theprecipitant (Pr) is CO₂ or carbonic acid. Surprisingly, inventors havefound that this precipitation can be performed at a pH of less than 7.In such an embodiment a precipitation step can be performed at a pHbetween about 6 and about 7. In a preferred embodiment a precipitationstep can be performed at a pH of about 6.7. The uncharged organic amineremaining in the supernatant 250 can, in turn, be regenerated 270 inthis process to form an organic amine cation that can form part of alixiviant 220 that can be used in the next iteration of the reaction.This recycling of the lixiviant greatly reduces consumption throughmultiple cycles of the process and advantageously reduces environmentalimpact and expense.

Other embodiments of the inventive concept can advantageously utilizethe selective complex formation and solubility of components of methodsof the inventive concept to recover different alkaline earth elementsfrom the same sample. One example of such a method is shown in FIG. 3.As shown, such a method can be a chain of reactions that are,essentially, one or more repetitions of the method shown in FIG. 1applied to a progressively depleted sample. In an example of such amethod 300, a sample 305 and a first lixiviant 310 are brought intocontact with each other. The first lixiviant 310 includes a firstorganic amine cation and a counterion, and reaction 315 with the sample305 produces a first depleted sample 320 and a first supernatant 325that includes a first alkaline earth cation, a counterion, and anuncharged organic amine. The first depleted sample 320 includesmaterials that were not reactive with the first lixiviant, which caninclude additional alkaline earth elements, other valuable materials,and unwanted contaminants. It can be separated from the firstsupernatant 325 by any suitable method, including settling, filtration,and centrifugation, either alone or in combination. The first alkalineearth cation can be recovered from the first supernatant 325 by anysuitable means, including electrodeposition, precipitation, and ionexchange. In a preferred embodiment of the inventive concept a firstprecipitant (Pr1) can used that generates an insoluble first alkalineearth salt and regenerates the first organic amine cation/counterionpair 330. In such an embodiment the uncharged first organic amineremaining in the supernatant 325 can, in turn, be regenerated 360 togive a first organic amine cation that can form part of a firstlixiviant 310 that can be used in the next iteration of the process.

The first depleted sample 320 can, in turn, be contacted 340 with asecond lixiviant 335 that includes a second organic aminecation/counterion pair. Reaction with the first depleted sample 320produces a second depleted sample 350 and a second supernatant 345 thatincludes a soluble second alkaline earth element cation/counterioncomplex and uncharged second organic amine. The second alkaline earthcation can be recovered from the second supernatant 345 by any suitablemeans, including precipitation, electrodeposition, and/or ion exchange.In a preferred embodiment of the inventive concept a second precipitant(Pr2) can used that generates an insoluble second alkaline earth saltand regenerates the second organic amine cation/counterion pair 355.

Such precipitants can be an H+ donating species suitable for forminginsoluble salts of alkaline earth elements while regenerating an organicamine cation, for example CO₂ or carbonic acid, chromic acid, orsulfuric acid. The regenerated second organic amine/counterion pair canin turn be recycled 365 for use in the next iteration of the process. Insome embodiments of the inventive concept the first precipitant and thesecond precipitant are the same species. In other embodiments of theinventive concept the first precipitant and the second precipitant aredifferent species. In a preferred embodiment of the inventive conceptthe first precipitant and the second precipitant are CO₂ or carbonicacid. In some embodiments of the inventive concept the second depletedsample 350 is subjected to further rounds of treatment with lixiviantsin order to recover additional valuable materials. This recycling of thelixiviants advantageously reduces the overall amount of organic aminesused as the process is repeated, which limits both the environmentalimpact of such operations and permits considerable savings in materials.

Another embodiment of the inventive concept that permits recovery of twoor more alkaline earth elements from a sample is shown in FIG. 4. Insuch a method 400 a sample 410 is contacted with a lixiviant 420 thatincludes a first organic amine cation/counterion pair and a secondorganic amine cation/counterion pair. This mixture 430 results in atreated sample 450 and a first supernatant 440. This first supernatantcan include a first alkaline earth element cation/counterion pair, asecond alkaline earth element cation/counterion pair, a first unchargedorganic amine, and a second uncharged organic amine. The first alkalineearth cation 460 can be recovered from the first supernatant 440 by anysuitably selective means, including precipitation, electroplating, orion exchange. In a preferred embodiment of the inventive concept, thefirst alkaline earth element can be recovered by adding a firstprecipitant (Pr1) that selectively forms an insoluble salt of the firstalkaline earth element (or cation) 460. For example, in a samplecontaining a mixture of magnesium and calcium, the calcium can berecovered in this step of the reaction by the addition of chromic acidas a first precipitant (P1) to form relatively insoluble calciumchromate (CaCrO₄); relatively soluble magnesium chromate (MgCrO₄) wouldremain in solution.

Recovery of the second alkaline earth cation from the second supernatant470 also yields a regenerated lixiviant. The second alkaline earthcation can be recovered from the second supernatant 470 by any suitablemeans, such as precipitation, electrodeposition, or ion exchange. Insome embodiments of the inventive concept, the second alkaline earthelement can be recovered by adding a second precipitant (Pr2) that formsan insoluble salt of the second alkaline earth element and completesregeneration of the lixiviant 480. For example, in a sample containing amixture of magnesium and calcium, the magnesium can be recovered in thisstep of the reaction from a supernatant resulting from chromic acidtreatment by the addition of CO₂ or carbonic acid as a secondprecipitant (P2) to form relatively insoluble calcium carbonate (CaCO₃).The regenerated lixiviant can in turn be recycled 490 in the nextiteration of the process.

In some embodiments of the inventive concept the first organic amine andthe second organic amine (and their respective cations) can be differentmolecular species with different acidities and/or specificities foralkaline earth elements. In other embodiments of the inventive conceptthe first organic amine and the second organic amine can be the samemolecular species, with selectivity between the first alkaline earthelement and the second alkaline earth element being provided by themethod used for their recovery from supernatants. For example,utilization of different precipitating species, utilization of the sameprecipitating species under different conditions (for example,concentration, temperature, pH, or a combination of these), utilizationof ion exchange media with different selectivities, or combinations ofthese approaches can be used to provide selective recovery of thealkaline earth elements of a sample. It should be appreciated that, asdescribed in the processes illustrated in FIG. 2 and FIG. 3, thatregeneration and re-use of the lixiviant through repeated iterationsadvantageously reduces the amount of organic amine needed, which limitsboth the environmental impact of such operations and permitsconsiderable savings in materials.

A specific example of the recovery of calcium from steel slag is shownin FIG. 5 and FIG. 6. FIG. 5 shows the composition of a typical steelslag, showing a complex mixture of various metal oxides includingcalcium oxide (CaO), which becomes calcium hydroxide (Ca(OH)₂) onexposure to water. Processing of such a steel slag is showndiagrammatically in FIG. 6. Initially, steel slag (or an alternativecalcium source) is ground 600 to less than around 125 μm. This greatlyincreases the surface area available for reaction. Water and lixiviantare mixed 610 in a suitable ratio, which can range from 1% to about 50%.The ground slag and aqueous lixiviant are mixed 620 and stirred oragitated for a time sufficient to form the calcium cation/counterionpair, in this instance approximately 10 minutes. The solid residue,which is depleted of calcium, is removed by filtration 630 and theliquid fraction or supernatant is processed by adding carbon dioxide (oran equivalent, such as carbonic acid) to precipitate calcium carbonate(CaCO₃) 640. This process also regenerates the lixiviant. The CaCO₃ canthen be prepared for further processing by washing, dilution into aslurry, and so on 660, while the regenerated lixiviant is recycled forre-use in the next iteration of the process 670.

Examples of the recovery of calcium by systems, methods, andcompositions of the inventive concept are shown in FIG. 7A-FIG. 7D. FIG.7A shows the change in pH over time as calcium is extracted fromlow-grade lime using monoethanolamine-HCl (MEACL) as the organic aminelixiviant. In this reaction 5 grams of low-grade lime was mixed with 50grams of water containing the lixivant at a lixiviant to calcium molarratio of 2.1:1, while stirring 400 rpm. The reaction was allowed toproceed for 23 minutes. FIG. 7B shows the results of a similar study, inwhich the pH was monitored over time as calcium is extracted fromlow-grade lime using glycine as the organic amine lixiviant. It shouldbe appreciated that as an amino acid glycine can be advantageouslyderived from biological sources and that, due to its zwitterionicnature, glycine can act as its own counterion. In this reaction 5 gramsof low-grade lime was mixed with 50 grams of water containing thelixiviant at a lixiviant to calcium molar ratio of 2.1:1, while stirringat 400 rpm. The reaction time was allowed to proceed for 24 minutes.FIG. 7C shows the results of recovery of extracted calcium using aprecipitant, in this instance CO₂. In this example pH was monitored asCO₂ was perfused through calcium extracted from low grade lime usingmonoethanolamine-HCl as the lixiviant. The reaction was performed for 11minutes as 100% CO₂ was perfused through the solution at 20 mL perminute at a temperature of 22° C., while stirring at 400 rpm.

A photomicrograph of an exemplary product from the extraction of calciumusing systems, methods, and compositions of the inventive concept isshown in FIG. 7D. The reaction was performed using 10 grams low-grade(˜50% CaO content) lime, which was treated with 19.7 grams ofmonoethanolamine-HCl in 100 grams water and stirred at 400 rpm for 30minutes. Solid residue was removed by filtration and the filtrateperfused with 100% CO₂ at a flow rate of 20 mL/min at a temperature of60° C., until the pH was less than 8 for 15 minutes. The yield ofprecipitated calcium carbonate (PCC) was 86%.

As shown in FIG. 8A-8B, the processes of the inventive concept canadvantageously be readily adapted to the infrastructure of currentprocessing plants. FIG. 8A shows a schematic of typical components andmaterial transfers of a commercial powdered calcium carbonate (PCC)plant. Limestone is received in a limestone bin and calcined in a kilnto produce calcium oxide. Flue gases from the kiln are processed in agas filter and scrubber. Calcium oxide from the kiln is transferred to aquicklime bin, and then to a slaker where it is mixed with water toproduce calcium hydroxide. Calcium hydroxide from the slaker istransferred to a cooling unit to remove heat from this exothermicprocess, and subsequently transferred to one or more reactors. Thereactors receive CO₂, part of which can be recovered from flue gas bythe scrubber, and mix it with the calcium hydroxide suspension. CO₂forms carbonic acid in the water of the suspension and slowly reactswith the solids of the calcium hydroxide suspension to produce calciumcarbonate. The solid calcium carbonate is transferred to a postscreentank and then a postscreen tank, and finally to a filter press in orderto remove unreacted material and a portion of the water. Materialrecovered by the filter press is transferred to a dryer for thoroughremoval of water to generate the powdered calcium carbonate product.

The arrangement and nature of the components in such a conventionalplant allows adaptation to lixiviant-based methods with minimaldisruption, as shown in FIG. 8B. As shown, new components and materialtransfer paths are shown with dotted lines. In the modified plant, theslaker receives a water/lixiviant mixture 800, which reacts with thecalcium hydroxide formed in the slaker to form a soluble calciumion/counterion complex that can be transferred to a cooling unit andsubsequently to a filterpress 810 that separates unreacted material 820from the calcium-containing solution, which is transferred 830 to one ormore reactors. Reaction with carbon dioxide, part of which can beobtained from the flue gas scrubber associated with the kiln, rapidlygenerates calcium carbonate in a solution-phase reaction, in the processregenerating the lixiviant. This regenerated lixiviant can be retrievedfrom the post screen tank and returned to the slaker for the nextiteration of the process. FIG. 8C shows how a multi (for example, 3 to5) effect evaporators 840 can be added to the effluent lines 850 fromthe filter presses of a lixiviant-adapted plant to concentrateregenerated lixiviant for re-use and to recover solvent (for example,water) 860 for use in washing the calcium carbonate produced by theprocess, in order to adjust and optimize the lixiviant concentrationwhile reducing material costs.

Advantageously, efficiencies of plants operated in such a manner can bevery high, as shown in FIG. 8D-8E. FIG. 8D shows mass balances for atypical iteration of a calcium isolation from steel slag. Only 7.22 kgof lixiviant is lost for 4,301 kg of 97.8% calcium carbonate produced.Over 99.9% of the lixiviant used in such a reaction is recycled fromprevious iterations. Similarly, FIG. 8E shows mass balances for atypical iteration of a calcium isolation from lime. Only 9.39 kg oflixiviant are lost for 4,301 kg of 99.8% pure calcium carbonateproduced. Over 99.85% of the lixiviant used in such a reaction isrecycled from previous iterations.

In exemplary processes described above the extraction of alkaline earthsalts from raw materials (leaving insoluble particulate waste) and theprecipitation of alkaline earth carbonates from the resulting solutionhave been separate, segregated processes. This approach can enableproduction of a pure calcium carbonate precipitate (PCC) to be used inindustries such as papermaking. However, in some embodiments of theinventive subject matter extraction and precipitation can occursimultaneously within a single container or enclosure as shownschematically in FIG. 9a and FIG. 9B. FIG. 9A depicts such a processusing a lixiviant. As shown, in such a process 900A, a raw materialcontaining an extractable alkaline earth salt (i.e. raw material) 910(for example, slag from steel processing, dolite, ash from municipalwaste, etc.), a lixiviant 920, and a source of carbon dioxide 930 (forexample, a carbon dioxide containing gas) are supplied to a vessel orother enclosure that serves as a reactor 940. In a preferred embodimentof the inventive concept the lixiviant 920 is supplied atsubstoichiometric amounts relative to the extractable alkaline earthsalt content of the raw material 910. It should be appreciated that onlya portion of the alkaline earth content of a raw material 910 can bepresent in the form of salts or other compounds that are subject oraccessible to extraction. The reactor 940 can also include provisionsfor the venting of excess or unreacted gas 950 (for example, non-CO₂ gascomponents originating from the source of carbon dioxide 930). Withinthe reactor 940 the reaction products (i.e precipitated alkaline earthcarbonate and regenerated lixiviant) along with unreacted and insolublewaste produce a mixture that is supplied to a separator 960. Theseparator 960 can segregate the reaction products produced in thereactor 940 and separate them from the waste or unreacted materials byany suitable means, including the application of centripetal force,magnetic attraction, settling by gravity, and/or filtration. Segregatedoutputs from the separator 960 include an alkaline earth carbonate 970,unreacted materials 980 derived from the raw material 910, andregenerated lixiviant 990. In some embodiments of the inventive concept,regenerated lixiviant 990 can be returned to the reactor 940 for evenhigher efficiency. It should also be appreciated that the unreactedwaste material, having been depleted of one or more alkaline earthelements, can be a commercially valuable material (having been,essentially, enriched in the remaining unreacted materials) and may becollected for further processing rather than disposed of.

FIG. 9B depicts an alternative embodiment of such a method, specificallyone that does include an added lixiviant. As shown, in such a process900B, a raw material containing an extractable alkaline earth salt (i.e.raw material) 910 (for example, slag from steel processing, dolite, ashfrom municipal waste, etc.) and a source of carbon dioxide 930 (forexample, a carbon dioxide containing gas) are supplied to a vessel orother enclosure that serves as a reactor 940. It should be appreciatedthat only a portion of the alkaline earth content of a raw material 910can be present in the form of salts or other compounds that are subjector accessible to extraction. The reactor 940 can also include provisionsfor the venting of excess or unreacted gas 950, which can, optionally,be directed back to the reactor 940 to serve as at least part of thecarbon dioxide source 930. Within the reactor 940 the reaction products(i.e precipitated alkaline earth carbonate and regenerated lixiviant)along with unreacted and insoluble waste produce a mixture that issupplied to a separator 960. The separator 960 can segregate thereaction products produced in the reactor 940 and separate them from thewaste or unreacted materials by any suitable means, including theapplication of centripetal force, magnetic attraction, settling bygravity, and/or filtration. Segregated outputs from the separator 960include an alkaline earth carbonate 970, unreacted materials 980 derivedfrom the raw material 910, and regenerated lixiviant 990. It should alsobe appreciated that the unreacted waste material, having been depletedof one or more alkaline earth elements, can be a commercially valuablematerial (having been, essentially, enriched in the remaining unreactedmaterials) and may be collected for further processing rather thandisposed of.

Other embodiments of the inventive concept can incorporate multipleseparators, as shown schematically in FIGS. 10A and 10B. FIG. 10Adepicts such a process using a lixiviant. In such a process 1000A rawmaterial containing an extractable alkaline earth salt 1010, and asource of carbon dioxide 1020, and a lixiviant 1030 are supplied to areactor 1040. In some embodiments of the inventive concept, raw materialcan be mixed with a lixiviant or lixiviant containing solution andsupplied to the reactor 1040 as a mixture or slurry. Within the reactor1040 the reactions in which the lixiviant generates soluble species fromaccessible alkaline earth salts of the raw material, formation ofinsoluble alkaline earth carbonates, and regeneration of the lixiviantspecies take place. After a suitable period of time the precipitatedalkaline earth carbonate, regenerated lixiviant, and particulateunreacted materials are transferred to a separator 1060, or optionally aseparator 1060 and a secondary separator 1062 or a plurality ofsecondary separators 1062, 1064. Such secondary separators can besimilar or identical to the separator 1060, or can differ in capacity,operating principle, or selectivity from the separator 1060. In someembodiments, secondary separators 1062 and 1064 can differ from eachother. Separation produces a segregation of the alkaline earth carbonate1070 from unreacted or waste materials 1080, and generates a stream ofregenerated lixiviant 1090 that is returned to the reactor 1040. Such aprocess obviates (at least partially) the need to add new lixiviant toeach performance of the process 1000 and advantageously results inconsiderable savings in time, material, and waste treatment costs.

FIG. 10B depicts an alternative process carried out in the absence ofadded lixiviant. In such a process 1000B raw material containing anextractable alkaline earth salt 1010 and a source of carbon dioxide 1020are supplied to a reactor 1040. Within the reactor 1040 the reactions inwhich the lixiviant generates soluble species from accessible alkalineearth salts of the raw material, formation of insoluble alkaline earthcarbonates, and regeneration of the lixiviant species take place. Aftera suitable period of time the precipitated alkaline earth carbonate,regenerated lixiviant, and particulate unreacted materials aretransferred to a separator 1060, or optionally a separator 1060 and asecondary separator 1062 or a plurality of secondary separators 1062,1064. Such secondary separators can be similar or identical to theseparator 1060, or can differ in capacity, operating principle, orselectivity from the separator 1060. In some embodiments, secondaryseparators 1062 and 1064 can differ from each other. Separation producesa segregation of the alkaline earth carbonate 1070 from unreacted orwaste materials 1080. In such embodiments unreacted carbon dioxide 1050can be collected and, optionally, returned to reactor 1040 as at leastpart of the carbon dioxide source 1020.

Still another embodiment of a method of the inventive concept is shownin FIG. 11, where the solubilization and precipitation reactions arepartially segregated from one another. In such a process 1100, rawmaterial that includes extractable alkaline earth salts (i.e. rawmaterial) 1110 is supplied to a primary reactor 1140. In someembodiments lixiviant or a lixiviant containing solution 1120 is alsosupplied to the primary reactor 1140. In still other embodiments, rawmaterial and lixiviant can be mixed and the resulting mixture or slurrysupplied to the primary reactor 1140. Following extraction of thealkaline earth from the raw material 1110, the reaction mixture istransferred to a primary separator 1160, which separates unreactedsolids from alkaline earth-bearing solution 1166. The alkalineearth-bearing solution 1166 is transferred to a secondary reactor 1167,where a source of carbon dioxide 1130 (for example, a gas that containscarbon dioxide) is added. This results in the formation of an alkalineearth carbonate in the form of a precipitate. The resulting precipitateslurry 1168 is transferred to a secondary separator 1169. Secondaryseparator 1169 produces a liquid fraction that contains regeneratedlixiviant, which can be in the form of a primary reactor stream 1190Aand/or in the form of a primary separator stream 1190B. The carbonatesolids 1170 segregated from the precipitate slurry 1168 by the secondaryseparator 1169 can be recovered for use or, alternatively, washed by theapplication of water or another suitable wash solution to the recoveredsolid (thereby producing a wash waste stream 1195) prior to recovery ofthe carbonate solid 370 from the secondary separator 1169.

Systems and methods of the inventive concept can efficiently extractalkaline earths from raw materials using only a fraction of thelixiviant utilized in prior art processes. In essence, theextraction-precipitation cycle is repeated continuously utilizing asmall (for example, sub-stoichiometric) amount of lixiviant that isregenerated during the cycle. In this way, the amine-containinglixiviant species acts a pseudocatalyst. Surprisingly, the inventorshave found that alkaline earths can also be extracted in the absence ofany added lixiviant.

In exemplary single step processes 900A, 900B, 1000A, 1000B, an 1100A asdescribed above, where alkaline earth carbonates are precipitated in thepresence of the raw material and/or extracted raw materials (which aregenerally supplied as particulates), efficient recovery or segregationof the desired alkaline earth carbonate is dependent upon distinguishingbetween particulate species in the resulting mixture. In preferredembodiments of the inventive concept, reaction conditions and rawmaterials are selected so that the particle density, particle shape,particle size, effective particle hydrodynamic radius, and/or magneticproperties of the particles of alkaline earth carbonate generated by theprocess and the density, particle shape, effective particle hydrodynamicradius, and/or magnetic properties particles of raw material (and/orextracted raw material) are sufficiently distinct to permit effectiveseparation (e.g. at least 50%, 60%, 70%, 80%, 90%, or greater than 90%segregation of the precipitated alkaline earth carbonate from the rawmaterial or extracted raw material). For example, in some embodiments ofthe inventive concept process conditions are selected such that theparticulates forming the alkaline earth carbonate precipitate can rangefrom 0.1 μm to 10 μm in size. In processes that utilize settling ordecantation for separation the product alkaline earth precipitate canhave a settling velocity that is substantially lower (i.e. 50% or less)than that of the extracted raw material, which can range in size from 50μm to 500 μm in diameter. For example, steel slags and extracted steelslags with a size range of 100 μm to 500 μm (with an average diameter of230 μm) was found to settle approximately 130 times more quickly than aproduct calcium carbonate precipitate particle have an average particlediameter of 15 μm. It should be appreciated that, for some rawmaterials, the density of the raw material, the extracted raw material,and the product alkaline earth precipitate can be similar, in which caseseparation behavior can be largely determined by particle size, shape,and/or effective hydrodynamic radius. In a preferred embodiment, thediameter of an alkaline earth carbonate precipitate can range from 250nm to 10 μm. The mean size and size distribution of such an alkalineearth carbonate product can be controlled, for example, by modulatingthe stirring speed within the reactor and/or the rate of CO₂ addition. Awide range of particle sizes is acceptable for the raw material, and theoptimal particle size for a given process may be determined by theeconomic impact of milling or grinding of the raw material and yield (aslarger particle sizes can be associated with reduced yield). In apreferred embodiment the average particle size of the raw material is200 μm. Suitable operating temperatures for single-step processes aresimilar to those of the two-step processes described above. In apreferred embodiment of the inventive concept a single-step process isperformed at approximately 60° C.

As noted in the processes described above, separation of theprecipitated alkaline earth carbonates and the extracted raw material isperformed in a separator. The separators referred to in the abovedescribed processes can utilize a wide variety of processes and/orphysical phenomena to segregate solids from liquids. Similarly, suitableseparators can perform segregation operations in a fixed volume or batchformat or on a continuous basis, as fits the requirements of theprocess. For example, suitable separators can use simple fractionationmethods such as gravitational settling, decanting, or desilting.Alternatively, suitable separators can perform filtration, for exampleusing press filters, rotary pressure filters, and/or vacuum beltfilters. In other embodiments, a separator can use centrifugal force,for example via a centrifuge or hydrocyclone. In still other embodimentsa separator can utilize magnetic effects (for example as provided by amagnet or electromagnet) to separate magnetically responsive (i.e.magnetic, diamagnetic, and/or paramagnetic) materials, for exampletreated steel slag particulates, from other materials that do notrespond to magnetic fields.

It should be appreciated that centrifugal separation techniquesadvantageously permit continuous separation, and can be configured tosegregate micron-scale particles of carbonate precipitates from largerand/or denser raw material residue particles from a particulate mixturegenerated by simultaneous performance of the above described extractionand precipitation reactions. In a preferred embodiment of the inventiveconcept, an alkaline earth carbonate production process can beconfigured such that raw material and a source of carbon dioxide aresupplied in a continuous fashion to a reactor supplied with a solutioncontaining a lixiviant species, with a stream of liquid containingsuspended particulates being directed to a separator that segregatesalkaline earth carbonate from extracted raw material and returns asolution containing the lixiviant species to the reactor. Alternatively,the raw material, the source of carbon dioxide, or both can be suppliedto the reactor in a pulsatile or intermittent fashion.

Another embodiment of the inventive concept is a system that isconfigured to perform the single-step methods described above. In someembodiments of the inventive concept, such a system can switch betweencontinuous and intermittent modes of operation to accommodate the needsof the operation and/or the availability of materials. Such a system caninclude a reaction enclosure, in which raw material, a lixiviantsolution, and a precipitant (such as CO₂ containing gas) are broughtinto contact with one another. Such a reaction enclosure can include oneor more sensors that provide data related to the progress of thereaction. For example a reaction enclosure can include a device forcharacterizing the pH of the reaction mixture, which as shown in FIG.16, FIG. 17A, and FIG. 17B changes during the course of the reaction.Other suitable sensors include an ion-selective electrode, densitometer,spectrophotometer, nephelometer, and particle characterization devicesbased on the Coulter principle. Such sensors can provide data to acontroller, which in turn can modulate the rate of the reaction bycontrolling the rate of introduction of raw material, lixiviant species,and/or precipitant to the reaction enclosure. The reaction enclosure isin communication with a separator. In some embodiments of the inventiveconcept such a reaction enclosure (or a portion thereof) can act as aseparator. For example, a reaction enclosure can be configured or have aportion that is configured for use in decanting (for example, beingconfigured as a vertically oriented cylinder or cone). In otherembodiments a separating device can lie within or be in fluidcommunication with the reaction enclosure. For example, a reactionenclosure can be in fluid communication with a filter device (such as afilter press) or a centrifugal separator (such as a centrifuge or ahydrocyclone). Such separating devices permit separation of theprecipitated alkaline earth salt from the extracted and/or unreacted rawmaterial, and from the liquid phase of the reaction mixture.

A system of the inventive concept can be configured to operate in adiscontinuous or in a continuous manner. When operated in adiscontinuous manner an amount of raw material, an amount of lixiviantspecies, and an amount precipitant are provided to the reactionenclosure and the reactions described above allowed to proceed. At leastone of these reactants (for example the raw material and/or thelixiviant species) is added to the reaction enclosure as a single bolus.This results in the formation of an alkaline earth containingprecipitant that is separable from the extracted raw material and asolution phase that includes the lixiviant species. At the completion ofthe reaction the reaction products are separated, and the processrepeated in a repetition of the reaction cycle. When operated in acontinuous manner raw material, lixiviant, and precipitant (for example,a CO₂ containing gas) are added to the reaction enclosure essentiallycontinuously (i.e. continuously or as a continuous series of small,distinct volumes), generating an equilibrium reaction mixture that isseparated essentially continuously (i.e. continuously or as continuousseries of small, distinct volumes). It should be appreciated that insuch an embodiment the addition of lixiviant species is inclusive of thereturn of regenerated lixiviant resulting from the separation process tothe reaction enclosure.

The inventors have found that such single-step processes (in whichextraction of the alkaline earth using a lixiviant is coupled withprecipitation of the alkaline earth and regeneration of the lixiviantspecies) are more efficient for extraction of alkaline earths, forexample calcium, from raw materials than traditional two-step orsegregated processes (in which extraction of the alkaline earth using alixiviant is decoupled from precipitation of the alkaline earth andregeneration of the lixiviant species). Surprisingly, the inventors havealso found that such single step processes can be performed in theabsence of an added lixiviant and still efficiently extract an alkalineearth (for example, calcium) from a raw material. This advantageouslyboth simplifies the process and eliminates exposure to lixiviantcompounds. Examples that illustrate this follow.

EXAMPLES Raw Materials and Methods

Two basic oxygen furnace (BOF) slags were utilized as raw materialsources of extractable calcium oxides/hydroxides in these experiments.One sample consisted of raw fines from U.S. Steel Lake Erie Works,Canada, while the other was a sample from a reject stream generated by aslag recycling plant at Ruukki Metals Raahe Works, Finland. Thecompositions of these slags, analyzed with XRF, are presented in FIG.19. Because the materials had been stored outdoors, they were calcinedfor three hours at 900° C. before extraction to reduce any material thatmay have already been carbonated by environmental factors.

The U.S. Steel slag was directly sieved to the desired size fractions,while Ruukki slag was first milled to smaller particle sizes and thensieved to the final desired size fractions. In the experiments aspecified amount of slag was mixed with a volume of ammonium chloridelixiviant solution of known concentration in a covered beaker with amagnetic stirrer. Solution pH was recorded using an Omega PHH-SD1 pHmeter.

Two types of process tests were conducted; two-step processes wereperformed as described in the prior art, and served to provide estimatesof the extractable calcium available through traditional processes.Towards this end the ammonium chloride lixiviant solution was providedin molar excess (see FIG. 20) to avoid stoichiometric limitations. Theraw material was first mixed with the NH₄Cl solution for 30 minutes.After removal of the residual extracted raw material by filtration,carbon dioxide gas was bubbled through the filtrate for 45 minutes. Theobtained carbonates were filtered from the solution, and the amount ofextractable calcium was determined by gravimetric analysis followingdrying the solids overnight at 80° C.

In one-step processes of the inventive concept, the raw material wasfirst suspended in water and the pH allowed to stabilize. Followingthis, sub-stoichiometric quantities of ammonium chloride salt (asdetermined from the results of the amount of extractable calciumrecovered from single step processes above) were added to the suspensionand carbon dioxide gas was fed to the reactor until solution pHdecreased to 8.00, after which the flow of CO₂ was stopped for 30minutes, allowing pH to increase and stabilize. To insure completeprecipitation of the calcium, the flow CO₂ gas was re-started whilemonitoring the pH decrease. The flow of CO₂ gas was continued for 10minutes after the pH reached 8.00. The experiment was finished withoutgas flow, recording the pH increase for seven additional minutes. Thesetime periods were selected based on the single step process describedabove to permit comparison between the different experiments, and can befurther optimized. The components of the final reaction mixture wereseparated by decanting followed by filtration. The lighter calcium-richfraction was first decanted from the reaction vessel to a filter, whilethe heavier slag residue particles remained at the bottom of the vesseland were filtered separately. Before weighing, the samples were driedovernight at 80° C.

In mass balance calculations it was assumed that all the observed massincrease resulted from captured carbon dioxide. The produced calciumcarbonate amount was calculated based on this assumption. The obtainedfractions were analyzed with SEM/EDX to characterize their compositionand particle structure. Select liquid samples were analyzed withICP-OES.

The experimental conditions from this series are listed in FIG. 20. Theslag-to-liquid ratio of the suspension was 100 g/L, temperature andpressure were ambient, and a pure CO₂ gas flow rate of 75 mL/min wasused.

Results

Calcium extraction and carbonate precipitation from different slagparticle size fractions (experiments 1-16) were studied with both one-and two-step methods. FIG. 12A shows that for the largest slag particles(500-1000 μm), the yields of the compared process alternatives wereequivalent. While yield increased as the raw material particle sizedecreased for both one-step and two-step processes, the increase inyield for the single-step process was dramatically greater than that ofthe two-step process for both raw materials. Surprisingly, as shown inFIG. 12B, in a one-step process with small <53 μm slag particles thecarbonate yield almost tripled compared to the prior art two-stepprocess (i.e. showed an almost 200% increase over and above the yield ofthe two-step process). With intermediate particle sizes the increase incarbonate production was 100-150%. Both U.S. Steel slag and Ruukki slagfollowed the same trend, suggesting a critical particle size, abovewhich both processes result in similar carbonate yields.

Interestingly, U.S. Steel slag with particle sizes 53-250 μm displayed aplateauing in carbonate yield. The yield increased once particle sizeswere reduced to below 53 μm. It is known that during slag formationcalcium tends to enrich in small particles. Thus, the U.S. Steel slagsize fractions may have differences in composition, with the sievingprocess resulting in a segregation of these different particlecompositions. Since the Ruukki slag sample was milled from largeparticles prior to sieving into particle size fractions, the differentfractions of the Ruuki slag may have a consistent composition and moredirectly show the effect of particle size.

FIG. 13 shows the masses of the separated fractions produced by one-stepprocesses applied to U.S. Steel slag (i.e. experiments 6-10). The massof the lower density “carbonate mixture” fraction increases withdecreasing slag particle size. This is not only because of the increasedrecovery of calcium carbonate, but also because the smaller slag residueparticles do not separate as efficiently from the carbonate particles bydecanting methods. This is especially true for the <53 μm slagparticles; the mass of “residue” (i.e. extracted raw material) wasdecreased, indicating that the extracted slag particles may have similarsettling properties to those of the produced calcium carbonate.

In experiments 1-19 the molar ratio of ammonium chloride and reactivecalcium oxide varied in part due to changes in the amount of extractablecalcium related to particle size effects. Earlier research has shownthat in the two-step process ammonium salt solution concentration doesnot significantly affect the calcium yield, assuming that the chosenconcentration exceeds the stoichiometric limits defined by Scheme 1.However, it is known that at ammonium salt concentrations above 1.5 Mthe selectivity towards calcium extraction diminishes, resulting inextraction of other elements such as Fe and Mn that can impactmass-based yield calculations.

On this basis it was expected that one-step calcium carbonation processyields would be largely independent of lixiviant stoichiometry. Toconfirm this, a series of experiments (experiments 21-26) were performedusing varying lixiviant molarities at a constant slag particle size(106-500 μm).

FIGS. 14-15 show that the molar ratio between the ammonium saltlixiviant and reactive calcium had no significant effect on theresulting carbonate yields above a certain minimum value during theone-step processes, even when substantially sub-stoichiometric amountsof lixiviant species are used. Only at very low values (0-0.01 molNH₄Cl/mol CaO), i.e. in case of almost pure distilled water as asolvent, was the calcium carbonate yield reduced. Surprisingly, fromFIGS. 12 and 14 it is also apparent that the carbonate yield fromone-step experiments was still higher (0.25 g/g) without lixiviant thanfrom two-step experiments utilizing a high lixiviant concentration(0.10-0.17 g/g). In some embodiments at least 5%, 10%, 20%, 30%, 40%,50%, 60% 70%, 80%, 90% or more than 90% of an alkaline earth (such ascalcium) can be recovered from a raw material by such single stepprocesses in the absence of an added lixiviant. Without wishing to bebound by theory, the inventors theorize that carbonate formation withinthe raw material slag particles acts to disrupt the particle structure,thereby exposing more alkaline earth for additional carbonation.

FIG. 16 shows the recorded pH values in two-step experiments 11-13 withRuukki slag. Extraction and carbonation are combined as one graph, eventhough the slag residue was filtered from the solution after 30 minutes.The variations in ammonium/calcium ratio affect the pH level; withsmaller particles (which presumably contain more accessible calcium), apH of roughly 10.5 is reached during extraction, compared to 9.7 withthe larger particles. The pH decrease during carbonation also requires alonger time for small particles.

Typical pH changes during a one-step reaction are shown in FIG. 17A,where different steps in the procedure are indicated by numbered arrows.In step 1, the slag raw material is added to water to make a suspension.The amine-containing lixiviant (for example, NH₄Cl) is added in step 2,and the initial application of CO₂ gas occurs in step 3. Note that theraw material suspension is strongly basic, and that the pH drops rapidlyas CO₂ is applied. The application of CO₂ is halted in step 4 andstarted again in step 5. Step 6 marks the termination of the reaction.Differences in pH measurements between the various experiments weresmall; larger amounts of reactive raw material were observed to resultin larger pH changes during all time periods. A more detailed study ofpH changes during application of CO₂ in a single-step process is shownin FIG. 17B shows a comparison of pH change deviations during the firstcarbon dioxide feed period in reactions performed at different lixiviantratios and with different sources of raw material. At low (0.01 molNH₄Cl/mol CaO) ammonium chloride concentration the pH changes at aslower rate than at relatively higher (0.2 mol NH₄Cl/mol CaO) for thesame size fraction of U.S. Steel slag. With Ruukki slag the pH decreaseis monotonic, while the U.S. slag causes an increase in pH, occurring3-5 minutes after the start of the gas feed, possibly indicating abiphasic reaction.

The one-step steel slag carbonation process has a number of advantagescompared to the two-step approach. Because the lixiviant is used insmaller amounts, the chemical cost is remarkably reduced even withoutrecovery and recycling of the ammonium salt solution, resulting also ina simpler process setup. In addition, the higher efficiency of theprocess reduces the amount of raw material that needs to be processed.As shown in FIG. 18 (which shows the difference in slag amount to beprocessed for production of one of ton calcium carbonate with one- andtwo-step methods), the prior art two-step process requires 3.1-4.5 tonsmore steel slag to produce 1 ton of carbonate product than is requiredfor the one-step process. This is essentially because, firstly, slag isprocessed and utilized to a larger extent, leaving a smaller amount ofresidue for waste handling. In addition, up to 140 kg more CO₂ per tonof slag can be captured in processing by the single-step processcompared to the traditional two-step process (depending on the slagparticle size). As such, the climate change mitigation potential isnoticeably increased. Finally, if the product is a calcium carbonatethat is utilized in steel manufacturing more calcium can be recycled atthe steel plant, thus reducing the need for virgin calcium rawmaterials.

It should be appreciated that the methods, systems, and compositionsdescribed above can be equally applicable to the processing of alkalineearth elements other than calcium, for example beryllium, magnesium,strontium, barium, and radium. Similarly, precipitating compounds otherthan carbon dioxide can be used in methods, systems, and compositions ofthe inventive concept, provided that they generate suitable precipitateson reaction with alkaline earth elements. Examples of suitableprecipitating compounds include sulfates, phosphates, and chromates. Itshould be appreciated that multiple iterations of the processesdescribed above can be applied sequentially or in series with suitableprecipitating compounds in order to generate a series of insolublealkaline earth salts from a single source material, and that individualmembers such a series of insoluble alkaline earth salts can havedifferent alkaline earth element compositions.

It should be apparent to those skilled in the art that many moremodifications besides those already described are possible withoutdeparting from the inventive concepts herein. The inventive subjectmatter, therefore, is not to be restricted except in the spirit of theappended claims. Moreover, in interpreting both the specification andthe claims, all terms should be interpreted in the broadest possiblemanner consistent with the context. In particular, the terms “comprises”and “comprising” should be interpreted as referring to elements,components, or steps in a non-exclusive manner, indicating that thereferenced elements, components, or steps may be present, or utilized,or combined with other elements, components, or steps that are notexpressly referenced. Where the specification claims refers to at leastone of something selected from the group consisting of A, B, C . . . andN, the text should be interpreted as requiring only one element from thegroup, not A plus N, or B plus N, etc.

What is claimed is:
 1. A method for the recovery of an alkaline earthfrom a raw material comprising; providing a raw material comprising analkaline earth to a reactor; in the same reactor, exposing the rawmaterial to a precipitant, thereby generating an alkaline earthprecipitate, and an extracted raw material; and separating the alkalineearth precipitate from the extracted raw material, wherein the method isperformed in the absence of an added lixiviant.
 2. The method of claim1, wherein the alkaline earth precipitate and the extracted raw materialare separated on the basis of particle diameter.
 3. The method of claim1, wherein the alkaline earth precipitate and the extracted raw materialare separated on the basis of at least one of particle characteristicsselected from the group consisting of particle density, particle shape,and effective particle hydrodynamic radius.
 4. The method of claim 1,wherein the separation is performed using a centrifugal separator. 5.The method of claim 1, wherein the separation is performed using afilter.
 6. The method of claim 1, wherein the separation is performedwithin a portion of the reactor that is configured as a settling tank.7. The method of claim 1, wherein the precipitant is selected from thegroup consisting of a gas comprising CO₂, phosphoric acid, a phosphatesalt, a carbonate salt, a bicarbonate salt, a sulfate salt, and sulfuricacid.
 8. The method of claim 1, wherein the raw material is introducedinto the enclosure in an essentially continuous manner.
 9. The method ofclaim 1, wherein the precipitant is introduced into the enclosure in anessentially continuous manner.
 10. The method of claim 1, whereinseparating is performed in an essentially continuous manner.
 10. Themethod of claim 1, wherein the extracted raw material is subjected tofurther processing.
 11. The method of claim 1, wherein the alkalineearth is calcium.
 12. The method of claim 1, wherein the raw material isselected from the group consisting of steel slag, lime, dolime,acetylene waste, and municipal ash waste.
 13. The method of claim 1,wherein at least 50% of alkaline earth content of the raw material isrecovered as the alkaline earth precipitate.